Gen Chem 2 ICE Table & Equilibrium Equation

Question

Determine the quantity of sodium acetate (CH3COONa) needed to create buffer solution at a particular pH. Do this by constructing an ICE table, writing the equilibrium constant expression, and using this information to determine the mass of starting material required. The value of Ka for CH3COOH is 1.8 x 10^-5.

Sodium acetate (CH3cooNa) is added to an existing 500.0 mL solution of 0.200 M CH3COOH to form a buffer with a pH equal to 5.000. Let x represent the concentration of CH3COO- in the water after the addition of CH3COONa. Fill in the ICE table with the appropriate value for each involved species to determine concentrations of all reactants and products.

Answer 1

Step 1: Determine the Desired Concentration of Acetate Ion (CH3COO-)

1. Use the Henderson-Hasselbalch Equation:

pH = pKa + log([A-]/[HA])

1. Calculate pKa:

pKa = -log(Ka)

pKa = -log(1.8 x 10^-5)≈ 4.74

1. Plug in the values into the Henderson-Hasselbalch equation:

5.000 = 4.74 + log([CH3COO-]/0.200)

1. Solve for [CH3COO-]:

5.000 - 4.74 = log([CH3COO-]/0.200)

0.26 = log([CH3COO-]/0.200)

10^0.26 = [CH3COO-]/0.200

1.82 ≈ [CH3COO-]/0.200

1. Solve for [CH3COO-]:

[CH3COO-] = 1.82 * 0.200≈ 0.364 M

Step 2: Calculate the Amount of Sodium Acetate Required

1. Determine the moles of CH3COO- needed:

Moles of CH3COO- = concentration * volume

Moles of CH3COO- = 0.364 M * 0.500 L

≈ 0.182 mol

1. Convert moles of CH3COO- to moles of sodium acetate (CH3COONa):
2. Sodium acetate dissociates completely in water, so moles of CH3COO- = moles of CH3COONa.

Moles of CH3COONa = 0.182 mol

1. Calculate the mass of sodium acetate required:
2. Molar mass of CH3COONa = 82.03 g/mol

Mass of CH3COONa = moles * molar mass

Mass of CH3COONa = 0.182 mol * 82.03 g/mol

Mass of CH3COONa ≈ 14.93 g

Final Answer

~ 14.93 grams.